1. Field of the Invention
The invention relates generally to the measurement of fluid flow and/or the control of fluid pressure in opened or closed fluid systems, and, in particular, to the measurement and control in closed systems of ultrafiltration in the hemodialysis procedure used in the treatment of kidney dysfunction and blood poisoning.
2. Description of the Prior Art
The normal kidney performs five basic functions, which are as follows: (1) removing the waste products of metabolism, (2) maintaining electrolyte equilibrium, (3) regulating water, (4) assisting in the regulation of blood pressure, and (5) assisting in the production of red blood cells.
The hemodialysis procedure is capable of accomplishing the first three functions only. Accordingly, removing waste and excess electrolytes are effected through diffusional mass transfer which is a function of the characteristics of the semipermeable membrane used and the concentration gradient across the semipermeable membrane. In addition, water is removed by imposing a pressure difference (transmembrane pressure) across the semipermeable membrane. This water, which is forced out of the blood into the dialysate, is called ultrafiltrate.
In most cases today, control of ultrafiltration is attempted through manual adjustment of blood flow rate and pressures, usually the pressure of the blood at the venuous return and/or the dialysate effluent pressure. The quantity of fluid actually removed is determined by weighing the patient before and after the hemodialysis treatment, computing the difference, and then correcting the difference for any extraneous causes for weight change, such as food or fluid intake. Control of ultrafiltration is based solely on the operator's experience in carrying out the above procedures. During the course of treatment, there is no dynamic means for determining actual ultrafiltration effected for the manual settings of pressure and flow. This is the more common technique used in hemodialysis treatment. Hence, there is a present need to provide improved method and apparatus for measuring and controlling ultrafiltration without effecting a new hemodialysis procedure.
Notwithstanding commonly used techniques, the ability to control ultrafiltration with a higher degree of certainty is much desired by the hemodialysis community. Consequently, researchers and hemodialysis equipment manufacturers have been working to provide solutions. Thus, some systems in current use provide the capability of measuring cumulative ultrafiltration. One such system features a regenerative dialysate supply means in which the dialysate volume is limited to the initial dialysate charge. Ultrafiltration increases the volume of the dialysate in the system and this change can be visually determined by means of a fluid level gage. However, all control is effected manually by conventional means, i.e., separate manual control of blood return pressure, blood flow rate and/or manual control of dialysate pressure. Generally, regenerative dialysate supply systems utilize an initial dialysate charge, for example six liters or less and have filter means in a fluid line to remove contaminants.
Another well known system uses a closed loop recirculating method which uses a fixed dialysate volume, for example, of 75 liters. The excess volume attributable to ultrafiltration is collected and measured in a graduated cylinder or its equivalent. Control of ultrafiltration is conventional for this negative pressure system which depends on blood pressure remaining constant for transmembrane pressure control. The suction pressure of the dialysate effluent (waste flow) is manually adjusted.
Notwithstanding a means for monitoring in one of the foregoing systems and a means for controlling transmembrane pressure in the other, there is a need for automated control of transmembrane pressure or ultrafiltration rate concurrently with metering and monitoring the ultrafiltration rate and the total quantity of ultrafiltrate removed.
The prior art, as indicated hereinabove, includes some advances in systems used for hemodialysis treatment. However, insofar as can be determined, no prior art system incorporates all of the features and advantages of the instant invention.